Furan is a platform chemical used in the synthesis of specialty chemicals. It is also known as a fuel additive.
Conventionally, furan is synthesized by vapor-phase decarbonylation of furfural in the presence of steam and Zn—Fe or Zn—Mn chromite catalyst at 400° C. with steam to furfural molar ratio of 1:5 to 1:10 and gas hourly space velocity (GHSV) of 500-1000 h−1. Furan yield of 85 to 90% on furfural was claimed (U.S. Pat. No. 2,374,149 and U.S. Pat. No. 2,776,981). Hydrogen and carbon dioxide are produced as by-products. High temperature operation in the conventional process results in breakdown of furan into heavy products, resulting in short-term deactivation of the catalysts. Further, when the process is operated at high temperatures, there is a corresponding requirement of heat energy and accordingly, the exit product vapors require a greater amount of cooling. In other words, the process becomes expensive.
According to U.S. Pat. No. 4,764,627, furan and derivatives can be produced by passing-vapors of furfural over a zeolite catalyst at a temperature (350-550° C.) and for a residence time effective to decarbonylate furfural. Furfural vapors are diluted with a carrier gas which is selected from the group consisting of hydrogen, carbon monoxide, carbon dioxide, methane, helium, argon, nitrogen and steam. Selectivity of furan, was low due to formation other products.
U.S. Pat. No. 4,780,552 teaches a process for preparation of furan by decarbonylation of furfural in the gas phase at elevated temperatures (250-400° C.), at a pressure of from 0.1 to 10 bar in the presence of hydrogen and a catalyst containing Pt, Rh or mixtures thereof and alkali metal (cesium). Furfural conversion of 90% and furan selectivity of 91-95% was obtained. But drop in conversion after 500 h of catalyst use is the drawback of this process.
According to U.S. Pat. No. 3,257,417 and U.S. Pat. No. 3,223,714, furfural is decomposed into furan and carbon monoxide on supported Pd surface at 200° C. This reaction is done in presence of an alkali metal carbonate or alkali metal acetate promoter. U.S. Pat. No. 8,404,871, US 2011/0201832 and US 2012/0157698 disclose the reaction of furfural on Pd over Al2O3 in presence of co-fed water and hydrogen at about 300° C. and with furfural to hydrogen molar ratio of 1:1 and weight hourly space velocity (WHSV) of furfural of 230 h−1 giving rise to furan with a yield of 95%. Hydrogen is co-fed to help volatilize furfural and to extend the catalyst life. The co-feed water enhances the conversion of furfural from 90 to nearly 100%.
2-Methyl furan is produced by hydrodeoxygenation/C═O hydrogenolysis of furfural. It has all the characteristics to be used a fuel additive. Methyl furan is produced through external supply of hydrogen which makes the process expensive.
U.S. Pat. No. 8,710,251 discloses synthesis of furan and related compounds by vapor-phase decarbonylation of furfural and derivatives using a palladium/metal aluminate catalyst. The process is effected by contacting furfural in vapor phase and hydrogen gas as co-feed at a temperature in the range of from about 270° C. to about 330° C. at ambient pressure.
Due to the industrial importance of furan and the drawbacks of prior-art processes including requirement of expensive hydrogen co-feed, need of alkali metal promoters and high temperature operation, a safe-to-handle and commercially economic process, green process is desirable.
The present invention overcomes the above-said drawbacks of the prior-art processes and discloses an improved process for producing furan and its derivatives from furfural at moderate temperatures and without using hydrogen-gas in the feed stream.
While the raw material furfural is conventionally obtained from petroleum feedstock, it can also be derived from the pentosan sugars of lignocellulosic biomass by methods known in the art (ChemSusChem, Year 2012, Vol. 5, pp. 751-761 and Sugar Technology, Year 2011, Vol. 13, issue 2, pp. 166-169). Use of biomass derived furfural leads to a sustainable process for production of furan.